Process and catalyst for the production of pyridine and alkyl derivatives thereof

ABSTRACT

A process for increasing the overall yield of pyridine or its alkyl pyridine derivatives during a base synthesis reaction is disclosed. The process comprises reacting a C 2  to C 5  aldehyde, a C 3  to C 5  ketone or a combination thereof, with ammonia and, optionally, formaldehyde, in the gas phase and in the presence of an effective amount of a particulate catalyst comprising a zeolite, zinc, a binder, and clay and optionally a matrix, wherein the catalyst has a L/B ratio of about 1.5 to about 4.0. Preferably, the zeolite is ZSM-5. A process for enhancing the catalytic activity of a zinc and zeolite containing catalyst to increase the overall yield of pyridine and/or its derivatives during a base synthesis reaction is also disclosed.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. application Ser. No. 15/435,714filed Feb. 17, 2017 and Ser. No. 14/437,997, filed Apr. 23, 2015, whichclaims the benefit of the filing date of International Application No.PCT/US2013/066593 filed Oct. 24, 2013, and U.S. Provisional PatentApplication No. 61/718,385 filed Oct. 25, 2012, entitled “PROCESS ANDCATALYST FOR THE PRODUCTION OF PYRIDINE AND ALKYL DERIVATIVES THEREOF”,the disclosure of which is hereby incorporated by reference.

FIELD OF THE INVENTION

The present invention relates to an improved process for pyridine basesynthesis, and to specified zinc containing zeolite based catalysts foruse in the same.

BACKGROUND OF THE INVENTION

Nitrogen-containing compounds are used as structural components ofpharmaceuticals and agrochemicals due to their high biological activity.Among these compounds, pyridine bases are produced in by far the largestquantity and are used in various applications such herbicides,insecticides, pharmaceuticals and adhesives.

The base synthesis of pyridine and its derivatives is well known. Theprocess generally involves reacting aldehydes and/or ketones withammonia in the gas phase using a heterogeneous catalyst either in afixed bed or fluidized bed reactor at temperatures ranging from about400° C. to about 450° C. The reaction generates coke and the catalysthas to be regenerated with air. The use of a fluidized bed provides auseful continuous regeneration system.

Catalysts used in pyridine base synthesis reactions have varied fromalumina either alone or as a support, to amorphous silica alumina (seee.g., U.S. Pat. Nos. 3,272,825; 3,946,020; and 4,089,863) and/or metalsubstituted silica alumina (see e.g., R. A. Sheldon and H. van Bekkum,Fine Chemicals through Heterogeneous Catalysis, Ed: Wiley p 277).However, in recent years, the focus has shifted to the use of so-called“shape selective” zeolite, e.g. aluminosilicates of a definite crystalstructure and pore size and characteristic, based catalyst systems. Amajor breakthrough in this area came with the use of the zeolite ZSM-5,also called “MFI”, which showed improved pyridine yields in the pyridinebeta reaction due to the shape selectivity offered by the size and twodimensional pore channels of the zeolite (see e.g., U.S. Pat. Nos.4,220,783; and 4,675,410). Improved pyridine yields were found in ZSM-5zeolites having silica/alumina ratios between 150-400 (see e.g., R. A.Sheldon, H. van Bekkum, Fine Chemicals through Heterogeneous Catalysis,Ed: Wiley p 277). Further improvements were seen in the development ofmetal substituted ZSM-5 zeolites. For example, zeolites ion-exchangedwith thallium, lead or cobalt showed increased yields of pyridine bases(see e.g., U.S. Pat. No. 4,810,794). Other metal substituted zeolitesused in pyridine catalysts have included ZSM-5 zeolites modified withone or more metal ions of zinc, tin or tungsten. (see for example, U.S.Pat. No. 5,218,122).

Because it uses inexpensive and widely available raw materials, basesynthesis of pyridine continues to provide good prospect to meet thegrowing demands for pyridine and its alkyl derivatives. However, thereremains a need for improved processes and catalysts which are useful toenhance product yields of pyridine and alkyl pyridine derivatives duringbase synthesis reactions.

SUMMARY OF THE INVENTION

The essence of the present invention lies in the discovery that arelationship exists between the Lewis (L) acid to Bronsted (B) acidratio (L/B ratio) and the catalytic activity of a zinc modified zeolitebased catalyst to increase the overall yields of pyridine during a basesynthesis reaction. Unexpectedly, it has been discovered that a zincmodified zeolite based catalyst having an L/B ratio ranging from about1.5 to about 4.0 exhibits a significant improvement in pyridine yield ascompared to yields obtainable using a zeolite based catalyst containingno zinc. Zinc modified zeolite based catalysts in accordance with theinvention also exhibit an activity for overall yield increases ofpyridine when compared to the activity of similarly zinc modifiedzeolite based catalysts having a L/B ratio of less than about 1.5 orgreater than about 4.0.

Accordingly, it is an advantage of the present invention is to provide aprocess of increasing the overall yields of pyridine or its alkylpyridine derivatives during a base synthesis reaction. In accordancewith the process of the invention, alkyl aldehydes and/or ketones arereacted with ammonia, and optionally, formaldehyde, in a gas phase inthe presence of an effective amount of a zinc modified zeolite basedcatalyst having an L/B ratio ranging from about 1.5 to about 4.0.

Another advantage of the present invention to provide catalystcompositions having improved catalytic ability to increase the overallyields of pyridine and its derivatives during a base synthesis process.Catalysts of the invention generally comprise a ZSM-5 and/or ZSM-11zeolite, zinc, a binder, clay and optionally a matrix material. In apreferred embodiment of the invention, the zeolite is ZSM-5. Catalystcompositions of the invention possess an L/B ratio ranging from about1.5 to about 4.0. Advantageously, higher overall yields of pyridine andits alkyl pyridine derivatives are achievable during a base synthesisreaction using the invention catalyst than yields obtainable using azeolite based catalyst containing no zinc or zinc modified zeolite basedcatalysts having an L/B ratio of less than about 1.5 or greater thanabout 4.0.

Yet another advantage of the present invention is to provide a method ofenhancing the catalytic activity of a zinc containing zeolite basedcatalyst to produce increased overall yields of pyridine and its alkylpyridine derivatives during a base synthesis reaction. The methodinvolves adjusting the components of the catalyst to provide specifiedL/B ratios, as measured by diffuse reflectance IR spectrum, in thecatalyst composition, which ratios unexpectedly correlate to an increasein the overall yields of pyridine bases during a base synthesisreaction.

These and other related advantages and variations of the detailedaspects of the present invention will become apparent from the followingdescription as described in further details below.

DETAILED DESCRIPTION OF THE INVENTION

The present invention is directed to improved processes and catalystcompositions for use therein which provides an increase in the overallyields of pyridine and its alkyl derivatives during a base synthesisreaction. In accordance with the process, base synthesis of pyridine andits alkyl derivatives is conducted in the presence of an effectiveamount of a particulate zinc containing zeolite based catalyst having aspecified L/B ratio. Catalyst compositions useful in the presentinvention generally comprises a ZSM-5 and/or a ZSM-11 zeolite, zinc, abinder, clay and optionally, a matrix material, in amounts sufficient toprovide the specified L/B ratio.

For purposes of this invention, the term “base synthesis” is used hereinto identify a process by which bases of pyridine or alkyl pyridine areprepared by reacting aldehydes and/or ketones with ammonia in the gasphase using a heterogeneous catalyst. Some examples of base synthesisreactions (and their common names where appropriate) include: thesynthesis of pyridine and beta-picoline from acetaldehyde andformaldehyde (the “pyridine-beta reaction”); the synthesis of alpha- andgamma-picoline from acetaldehyde (the “alpha-gamma reaction”); thesynthesis of 2,6-dimethylpyridine (“2,6-lutidine”) from acetone andformaldehyde; the synthesis of 2,4,6-trimethylpyridine (“sym-collidine”)from acetone alone or with acetaldehyde; the synthesis of pyridine andbeta-picoline from acrolein alone or with acetaldehyde; the synthesis of3,5-dimethylpyridine from propionaldehyde and formaldehyde; and thesynthesis of beta-picoline from acetaldehyde, formaldehyde andpropionaldehyde. Many others are known and reported or practiced in theart, and are equally considered within the scope of the description andinvention herein.

Zeolites useful to prepare catalysts in accordance with the inventiongenerally include ZSM-5 and/or ZSM-11 zeolites. In a preferredembodiment of the invention, the zeolite is ZSM-5.

In one embodiment of the invention, the zeolites useful to preparecatalyst of the invention possess a silica to alumina ratio of about 100or less. In a preferred embodiment, the zeolites have a silica toalumina ratio of about 20 to about 80. In an even more preferredembodiment of the invention, the zeolites possess a silica to aluminaratio of about 28 to about 55.

Primarily, the binder performs the all important function of holding thecomponents of the catalyst compositions together. However, it is withinthe scope of the invention that the binder may also provide somecatalytic activity. Suitable binders contemplated for use in thecatalyst compositions of the invention typically include, but are notlimited, to silica, alumina, silica-alumina and combinations thereof. Ina preferred embodiment, the binder is alumina. Preferably, the aluminabinder is a gamma alumina that has been derived from an aluminum sol,colloidal alumina, peptized alumina, aluminum chlorohydrate and/or otheraluminum precursors.

Catalysts useful in the present invention also include clay. Whilekaolin is the preferred clay component, it is also contemplated thatother clays, such as pillard clays and/or modified kaolin (e.g.metakaolin), may be included in catalyst compositions useful in thepresent invention.

It is also within the scope of the invention, that in additional toclay, a matrix material may optionally be present in catalystcompositions useful in the present invention. When present, suitablematrix materials include metal oxides, e.g. alumina, silica,silica-alumina, oxides of transition metals and combinations thereof.Preferably, the matrix materials include alumina, silica, silica-aluminaand combinations thereof.

Catalyst compositions useful in the present invention have an L/B ratioof about 1.5 to about 4.0. In a preferred embodiment of the invention,the catalyst compositions have an L/B ratio ranging from about 2.0 toabout 3.6. The L/B ratio may be obtained by adjusting the concentrationof any or all of the catalyst components during catalyst formulation toprovide the desired L/B ratio. The L/B/ratio may be measured usingdiffuse reflectance IR spectrum to determine the ratio of the height ofthe 1450 cm-1 peak L=(Lewis acid sites) to the 1550 cm-1 peakB=(Bronsted acid sites).

The particulate catalyst compositions of the invention are useful in abase synthesis process typically operated in a fixed bed or fluidizedbed reactor, e.g. FCC catalytic cracking unit, to achieve an overallincrease in pyridine and alkyl pyridine yields. The catalystcompositions are typically in the form of spherical particles and have aparticle size and an attrition property sufficient to affectfluidization properties within a fixed bed or fluidized bed reactor.When used in a fluidized bed reactor, catalyst compositions of theinvention will typically have a mean particle size of about 40 μm toabout 200 μm. In a preferred embodiment of the invention, the catalystcompositions have a mean particles size ranging from about 60 μm toabout 120 μm.

Catalyst compositions used in the present invention will possess anattrition resistance, as measured by Davison Index (DI), sufficient tomaintain the structural integrity of the compositions in the fixed bedor fluidized bed reactor. Typically, a DI value of less than 20 will besufficient. In a preferred embodiment of the invention, the DI value isless than 10.

The amounts of each of the components in the catalyst compositions willvary depending on such factors as the desired L/B ratio, the particlesize, the attrition resistance, the reactor to be used, etc. Generally,the amounts of zeolite, zinc, binder, clay and optionally matrixcomponents present in the catalyst compositions used in the inventionwill vary within a wide range, e.g. about 1-99% by weight, respectivelyfor each component, based upon the total weight of the composition,provided however, that each component is used in an amount sufficient toprovide the desired L/B ratio, particle size and attrition resistancefor use of the final catalyst composition in a fixed bed or, preferably,a fluidized bed reactor. In a preferred embodiment of the invention, theamount of zeolite ranges from about 35 wt % to about 50 wt % of thecatalyst composition. The binder amount ranges from about 10 wt % toabout 30 wt % of the catalyst composition. The clay component willpreferably comprise from about 30 wt % to about 50 wt % of the totalcatalyst composition. When used, the matrix material will typicallycomprise the remainder of the catalyst. All of said weight percentagesrecited herein above is based on the total weight of the final catalystcomposition.

Zinc may be incorporated into the catalyst composition by treatment onthe zeolite before or after the zeolite is formulated with the binder,clay and optionally matrix components to prepare the final catalystcompositions. Alternatively, zinc may be incorporated during catalystformulation as a component of the catalyst. Further, zinc may beexchanged onto the preformed catalyst following catalyst formulation.

Where the zeolite is treated with zinc prior to catalyst formulation,the zeolite may be modified through treatment with metal ions orcompounds of zinc. Suitable zinc compounds include, but are not limitedto, soluble salts such as nitrates, halides or acetates. Treatment ofthe zeolites may be carried out in any number of ways known in the art(such as for example, U.S. Pat. No. 5,218,122, said patent hereinincorporated by reference in its entirety) and may be carried outseveral times if desired to ensure substantial metal uptake on thezeolite.

In one embodiment, the zeolite is added to an aqueous solution of thedesired amount of zinc compound in stoichiometric excess to obtain amixture. Optionally, the mixture is heated at a predeterminedtemperature and time with stirring. The mixture is filtered, rinsed,dried and then calcined at elevated temperature, e.g. about 100° C. toabout 600° C. to obtain the modified zeolite.

In another embodiment of the invention, a physical mixture of thezeolite and the desired zinc salt is accomplished either dry or in thepresence of water in an amount sufficient to obtain a paste or similarconsistency, by blending, mixing or other suitable physical means. Theseand other similar procedures are well known within the catalysis artsand are all within the scope of the invention.

The final catalyst compositions may be prepared by any conventionalmeans known in the catalysis arts. In a preferred embodiment of theinvention, catalyst compositions in accordance with the presentinvention are formed from an aqueous slurry which comprises an amount byweight of the zeolite, optionally zinc, binder, clay and optional matrixmaterials. The amounts of the catalyst components, i.e. zeolite,optionally zinc, binder, clay and optional matrix materials, areadjusted in the slurry to provide an amount of each component sufficientto obtain the desired L/B ratio, particle size and attrition resistancein the final catalyst composition.

Zinc may be present in the slurry as zinc ions pre-exchanged on thezeolite prior to incorporation into the aqueous slurry as describedherein above. In the alternative, zinc may be present in the aqueousslurry as a component thereof in the form of a salt solution of zinc,e.g. zinc nitrates, halides and/or acetates as described herein above.

The aqueous slurry is subjected to a spraying step using conventionalspray drying techniques. During the spray drying step, the slurry isconverted to a particulate solid composition. The spray dried catalystparticles typically have an average particle size on the order of about40 to about 200 μm. Following spray drying, the catalyst particles arecalcined at temperatures ranging from about 150° C. to about 600° C. fora period of about 4 hours to about 10 minutes.

Where the zinc has not been previously incorporated into catalyst, thepreformed catalyst particles may be ion exchanged with zinc, in theamount desired in the final catalyst composition. Alternatively, thecatalyst particles may be impregnated, e.g. via incipient wetness, withan aqueous salt solution of zinc to impregnate zinc ions onto thecalcined catalyst particles. The catalyst particles may thereafter bywashed, preferably with water and the washed catalyst particles areseparated from the slurry by conventional techniques, e.g. filtration,and dried to lower the moisture content of the particles.

The process of the invention provides an increase in the overall yieldsof pyridine or its alkyl pyridine derivatives produced during a basesynthesis reaction. Significant improvement in overall pyridine yields,i.e. greater than 2%, were achieved when compared to yields obtainedusing a zeolite based heterogeneous catalyst which contain no zinc.Improved overall pyridine yields, i.e. greater than 70%, were alsoachieved over similar zinc containing zeolite based catalyst having aL/B ratio of less than about 1.5 or greater than about 4.0.

In accordance with the process of the invention, alkyl aldehydes and/orketones are reacted with ammonia, and optionally, formaldehyde, in a gasphase in the presence of an effective amount of a particulate catalystcomposition as described hereinabove in fixed bed or fluidized bedreactor to achieve an unexpected overall increase in yields of pyridineand it alkyl derivatives. The equipment set up and operation offluid-bed reactors vary according to many factors tied to the particularreaction under consideration. The same are readily constructed by thoseof ordinary skill in the art, and are all within the scope of theinvention herein. Reaction parameters such as temperature, feed moleratios, feed velocity and contact time and the like vary over a widerange of operable conditions also well known and within the scope of theinvention.

As previously discussed, many base synthesis processes are known and arealso contemplated to be within the scope of the invention herein. Inaddition to the specific Examples below and to the disclosuresincorporated by reference above, for the pyridine-beta synthesis it isgenerally preferred that a feed of formaldehyde to acetaldehyde in amole ratio of at least about 1:1 is used. The addition of methanol tothe extent of about 5 to 70% of the formaldehyde component is alsopreferred, as originally described in U.S. Pat. No. 2,807,618. At leasta portion of the formaldehyde can further be replaced byparaformaldehyde or sym-trioxane, and water can be present as desired toprovide a stable, storable solution. Ammonia is supplied in a ratio ofat least about 0.6:1 to the total organic components in the feed, with arange of about 0.7 to 1.5 being more preferred and about 0.8 to 1.2being most preferred from testing to date. The feed rate is in turnchosen to give good fluidization of the bed, usually in the range of asuperficial velocity between about 0.3 to 4.0 ft./sec. Temperature ofthe reaction is preferably between about 350° C. and 550° C. morepreferably between about 400° C. and 500° C. and most preferably atabout 450° C. The products of the reaction, being pyridine andbeta-picoline, are condensed and separated into pure compounds by dryingand distillation as is well known in the art. By way of a secondexample, the alpha-gamma reaction is preferably carried out in much thesame way except that formaldehyde and methanol are left out of the feedmixture.

To further illustrate the present invention and the advantages thereof,the following specific examples are given. The examples are given asspecific illustrations of the claimed invention. It should beunderstood, however, that the invention is not limited to the specificdetails set forth in the examples.

All parts and percentages in the examples as well as the remainder ofthe specification that refers to solid compositions or concentrationsare by weight unless otherwise specified. However, all parts andpercentages in the examples as well as the remainder of thespecification referring to gas compositions are molar or by volumeunless otherwise specified.

Further, any range of numbers recited in the specification or claims,such as that representing a particular set of properties, units ofmeasure, conditions, physical states or percentages, is intended toliterally incorporate expressly herein by reference or otherwise, anynumber falling within such range, including any subset of numbers withinany range so recited.

EXAMPLES Example 1

Catalysts A, B, C, D and E were prepared using ZSM-5 with asilica/alumina ratio of 28 or 55. Zinc chloride was added into anaqueous slurry of zeolite, an alumina binder and clay and the slurry wasspray dried using standard spray drying procedures. The spray driedparticles were calcined at a temperature of 593.3° C. (1100° F.) toobtain the final catalysts. Compositions of the catalysts followingspray drying and calcination were as shown in Table 1 below.

TABLE 1 CATALYST ZSM-5 Alumina Clay ZnO A 39.4* 11.8 47.3 1.42 B 39.0*11.7 46.8 2.32 C 39.4** 11.8 48.3 0.53 D 39.4** 11.8 47.8 1.12 E 39.4**11.8 47.3 1.69 *silica/alumina = 28 **silica/alumina = 55

Example 2

The catalyst samples obtained in Example 1 above and a control catalystsample (no zinc) were analyzed using diffuse reflectance IRspectroscopy. The procedure was as follows: Approximately one gram ofsample was placed in a ceramic crucible which was placed in a speciallydesigned quartz cell. The samples were calcined for one hour at 500° C.then for one hour under vacuum. The samples were returned to roomtemperature and were exposed to a pyridine saturated stream of heliumfor 30 minutes. The physisorbed pyridine was then removed by heating thesamples to 200° C. for two hours under vacuum. Peak height was measuredby placing the curser at the peak maximum and adjusting the baseline.The L/B (Lewis/Bronsted) ratio was measured by comparing the height ofthe 1450 cm-1 peak L=(Lewis acid sites) to the 1550 cm-1 peakB=(Bronsted acid sites). Results were as recorded in Table 2 below.

TABLE 2 CATALYST L/B RATIO No Zinc 0.57 A 3.3 B 6.0 C 1.1 D 2.1 E 3.1

Example 3

The performance of the catalysts was evaluated and correlated to L/Bratios. The procedure for testing the catalysts in a fluidized bedreactor was as described in U.S. Pat. No. 4,675,410, the disclosure ofwhich is herein incorporated by reference in its entirety. The catalystformulations as described in Example 1 above and the control catalystwere loaded into the fluid bed reactor. The catalysts were heated undera nitrogen flow of ˜60 liter per hours to a temperature of ˜450° C. Amixture of acetaladeldhyde and formaldehyde was passed through avaporized into the reactor. The nitrogen flow into the reactor wasreplaced with an ammonia flow at a rate of ˜111 g/hr. Pyridine yieldswere calculated as Yield %=total C atoms in Product×100/total C atoms infeed. Results are recorded in Table 3 below.

TABLE 3 CATALYST L/B Yield improvement Control - no zinc 0.57 — A 3.32-4% B 6.0 0-1% C 1.1 1-2% D 2.1 2-4% E 3.1 2-4%

The data shows that catalysts having an L/B ratio between about 1.5 toabout 4.0 achieved overall yield improvements of 2% or greater ascompared to the control which contained no zinc. While catalystcontaining zinc but having an L/B ratio outside of the range of theinvention, i.e., of about less than 1.5 and greater than about 4.0,showed increase yields as compared to the control, they showed inferioroverall yields of pyridine bases when compared to yields obtained usingthe process and catalyst of the present invention.

The invention claimed is:
 1. A base synthesis process for thepreparation of pyridine or its alkyl pyridine derivatives comprisingreacting a C₂ to C₅ aldehyde, a C₃ to C₅ ketone or a combinationthereof, with ammonia and, optionally, formaldehyde, in the gas phaseand in the presence of an effective amount of a particulate catalystcomprising a zeolite selected from the group consisting of ZSM-5, ZSM-11and combinations thereof, zinc, a binder and clay, wherein the catalysthas a L/B ratio of about 1.5 to about 4.0.
 2. The process of claim 1wherein the catalyst further comprises a matrix material.
 3. The processof claim 1 wherein the zeolite is ZSM-5.
 4. The process of claim 1wherein the organic reactants are acetaldehyde and formaldehyde, andcomprising the additional step of recovering pyridine and beta-picolineas the products of said process.
 5. The process of claim 1 wherein thezeolite has been treated with a compound of zinc prior to incorporationinto the catalyst composition.
 6. The process of claim 1 wherein acompound of zinc is incorporated as a component of the catalyst duringformulation of the catalyst composition.
 7. The process of claim 1wherein a compound of zinc is ion exchanged on preformed catalystparticles.
 8. The process of claim 6 wherein the compound of zinc isselected from the group consisting of nitrate, halides, acetates andcombinations thereof.
 9. The process of claim 1 wherein the catalyst hasan L/B ratio of about 2.0 to about 3.6.
 10. The process of claim 1wherein the binder is an alumina binder.
 11. The process of claim 1wherein the zeolite has a silica to alumina ratio of about 100 or less.12. The process of claim 11 wherein the zeolite has a silica/aluminaratio of from about 20 to about
 80. 13. The process of claim 3 whereinthe zeolite has a silica/alumina ratio of about 28 to about
 55. 14. Theprocess of claim 1 wherein the zeolite is present in an amount rangingfrom about 35 wt % to about 50 wt % based on the total weight of thecatalyst composition.
 15. The process of claim 1 wherein the binder ispresent in an amount ranging from about 10 wt % to about 30 wt % basedon the total weight of the catalyst composition.
 16. The process ofclaim 1 wherein the clay component is present in an amount ranging fromabout 30 wt % to about 50 wt % based on the total weight of the catalystcomposition.
 17. The process of claim 1 wherein the particulate catalysthas a particle size sufficient for use in a fluid bed reactor.
 18. Theprocess of claim 17 wherein the particulate catalyst has a particle sizeranging from about 40 μm to about 200 μm.
 19. The process of claim 1wherein the particulate catalyst has a Davison Index (DI) of less than20.
 20. The process of claim 1 wherein pyridine and beta-picoline arerecovered as the products of said process.